The present invention relates to a system for the transmission of information messages which are encoded in the form of digital signals wherein a code is selected which facilitates the testing of each information bit, including a central station and a series of substations at which the information messages of the central station are selectively deliverable through the electrical power supply wiring as the transmission path which is utilized by further similar systems. Each substation, due to an erroneously recognized information bit, will terminate the further information evaluation, whereby each of the information messages evidences a selectable subsequence of digital signals which is specific with respect to the applicable system, which preferably occurs near the beginning of the total sequence of digital signals representing the information message.
2. Discussion of the Prior Art
A system of that type is commercially available and is utilized as a socalled inherently wireless house cable system. This system is designated as "inherently wireless" because, for information transmission between the central station and the substations no separate wiring network is employed, but the phase conductors of the already-installed electrical power supply are used as the transmission path, wherein the supply voltage serves for the synchronization of the central station and the substations. Such a system is designated as a "house wiring system" inasmuch as, while in a building or even only in an apartment electrical appliances are selectively controlled by the substations associated with these appliances from the central station such as, for instance, switched on or off, checked with respect to their condition or, in the case of electrical illuminating members, there can be carried out a dimming procedure. Serving as the addresses or operational commands for the transporting information messages for the substations associated with the individual appliances are carrier frequency transmitted digital signals, in which the carrier frequency is high in comparison with both the supply voltage frequency and the base frequency of the digital signals. The coding of the digital signals is hereby selected so that there is employed a code particularly adapted for the testing of each informational bit. This requirement is fulfilled by a redundant code. Each information message which is employed within the framework of such a specialized system contains in the first section a selectable subsequence of digital signals which is specific to the respective system, which is designated as the "house code". Thereby it becomes possible that, when a number of apartments are present, for example within one building, in each of which there presently is utilized such a system having the same carrier frequency, to preclude the mutual interference of such systems, since each substation of such a system will only respond when the information telegram contains the "house code" selected for that apartment as well as the special address of the substation. Naturally, the same reasoning is also valid for the same types of systems which are located in neighboring buildings.
However, the possibility cannot be excluded that neighbors which utilize such similar kinds of systems will intentionally or inadvertently utilize a "house code" which has already been selected by another neighbor, and to thereby be able to initiate control procedures in the house or in the apartment of the other neighbor. In order to preclude such a foreign or outside interference, it is common to arrange carrier frequency blocks at the electrical meter of each such apartment or building utilizing such a system. Such carrier frequency blocks must be included as added components in such a system and installed by a skilled worker, by means of which there are encountered additional expenses.